With CF it's all about durability and compatibility with pro cameras, speed should be about the same with both. Advantage of sd cards is compatibility in everyday devices like integrated slots in computers, tablets, etc.

Speed has been my biggest concern. I've been more worried about pin issues damaging the camera than the card, so that is moot for me.

It surprises me that the costs seem similar when SD has to be so much more minimized than CF.

In terms of pure write speed, the Lexar 1000x UDMA7 cards are the fastest cards out there in a UDMA7 camera, barring the XQD which right now only the Nikon D4 supports. Most SDXC UHS-1 cards will still give great performance, in a camera with a UHS-1 slot, but they still won't perform quite as high as the top performing CF card.

Personally, I can't wait for the XQD, and I hope the next Canon and Nikon's support them, even if it does mean needing to buy all new cards for the camera. Of course, for me that's 3-5 years off most likely, so by then there should be a good number of cards and readers out there.

I've always preferred CF for many reasons, not the least of which is speed and physical size. The CF cards I have tend to be faster than the SD counterparts rated for the same speed. Without a lot of careful testing it's hard to quantify this but I've read detailed accounts on the web of folks who have tested them heavily and the CF cards always outperformed the SD cards. I suspect this is why the faster cameras like the 7D and 1DX still use CF as a primary format. Also, all the pins on a CF card are for better grounding. This equates to better more stable data transfer. And finally, CF cards are just a lot easier to manage in the field. At least to me they are.

Anyway, that is my OPINION, please let's not start a big war on formats and specs. It boils down to personal preference because BOTH are so close that it really doesn't matter. And UHS-1 SD cards are very fast. Much better than the SDHC cards that I tend to look down on.

I use a SDXC card in my 5D MK III (its not UHS-1). I do not try to shoot the high FPS rate, so its no issue. If I were shooting high FPS, I'd merely stop recording to both cards.

If you think about it, when writing to both cards, the speed of the slowest card will limit the writing speed. Thats almost always the SD card.

Unfortunately, the design of the 5D MK III was apparently frozen before SDXC UHS-1 cards arrived. Its unfortunate, but true.

True, but looking out even 1-2 years and it should have been pretty obvious that UHS-1 cards were coming, and quickly. Besides, an SDXC UHS-1 slot would work just fine with the slower speeds. Personally, I suspect that the DIGIC 5+ only has 1 super-high speed storage interface, so the SD slot has to hang off of a slower bus. The 1D-X doesn't have this problem since it has 2 DIGIC 5+ which gives it the 2 super-high speed interfaces, 1 per chip.

I'm hijacking my own thread, but it seems that this would be an easy fix for some users from Canon.

Have the camera record to the CF card at max speed, and then copy from the CF card to the SD card when there is downtime. If the CF card could read/write at maximum speed at the same time, then this would be seamless.I don't know if the DIGIC 5+ just refers to the processor or the entire logic board, but you'd imagine that Canon could designed it so that the DIGIC 5+ dump the data to a second system that handles the CF/SD I/O.

I'm hijacking my own thread, but it seems that this would be an easy fix for some users from Canon.

Have the camera record to the CF card at max speed, and then copy from the CF card to the SD card when there is downtime. If the CF card could read/write at maximum speed at the same time, then this would be seamless.I don't know if the DIGIC 5+ just refers to the processor or the entire logic board, but you'd imagine that Canon could designed it so that the DIGIC 5+ dump the data to a second system that handles the CF/SD I/O.

Not sure, but the DIGIC 5+ probably uses a DMA (built into pretty much all modern, reasonably high performing processors these days) controller to transfer from RAM to the memory card(s).

In terms of having it automatically copy from CF to SD, the big challenge I think is that you never know when someone is going to start doing a big burst of images which need flushing to the CF card. Personally I'd never use that functionality, it could potentially be error prone where the camera thinks it's successfully copied something from the CF to the SD card, but then it's only partially there, or not at all and deletes it from the CF card. Oops. I'd rather the camera only ever write to the memory card, except when I tell it to delete/format.

I appreciate the concern with data integrity, but it could be possible for the camera to verify the copies with an MD5 or SHA-1 process. I think you would also design it to maintain the CF copy as a master.

That aside, thank you everyone for your comments on the benefits and cons of CF vs SD.

The SD UHS-1 cards truly surprised me! I also learned that the SDXC readers in Retina MacBook Pro's are direct to the logic board and transfer at 2.5GT/s, which is well into the GB/s range. The old MacBook Pro's used to have their SDXC readers attached to the USB 2.0 bus, so they were limited to a theoretical maximum of 60MBps.